Damp plaster

amandstu · 10-09-2019 2:52pm #1

I have an interior wall which got damp as a result of a leak in the chimney stack above.

Even though that leak has been fixed the plaster will still not take paint without yellowing it immediately and in fact the plaster is still damp some 4 or 5 months later.

Beneath the plaster ,the rendering is dry but the plaster itself shows no sign of ever drying out.

Is that common .....for the plaster to be damaged by dampness so that it never dries even when the original dampness has been fixed ?

Is replastering the only cure?(I am not going to double line the wall-if that is the còrrect term)

Doop · 10-09-2019 5:45pm

You can buy paint specifically for painting over damp patches... I would say a coat of that and then regular paint and you should be good

amandstu · 10-09-2019 6:07pm

Doop wrote: »

You can buy paint specifically for painting over damp patches... I would say a coat of that and then regular paint and you should be good

Any difference between those products and oil based paints such as white gloss or undecoat?

punisher5112 · 10-09-2019 6:09pm

You need to dehumidify....

If that doesn't work you may need to remove and allow dry out. Then re plaster effected area.

Roger Mellie Man on the Telly · 10-09-2019 7:02pm

Sounds like you still have a leak, or a leaking pipe.

Don't use damp proof paint - you're just diverting the problem.

dok_golf · 10-09-2019 9:47pm

Roger Mellie Man on the Telly wrote: »

Sounds like you still have a leak, or a leaking pipe.

Don't use damp proof paint - you're just diverting the problem.

This..

fred funk }{ · 11-09-2019 7:06am

Roger Mellie Man on the Telly wrote: »

Sounds like you still have a leak, or a leaking pipe.

Don't use damp proof paint - you're just diverting the problem.

Yes. Sounds like there's still a leak somewhere.

cheif kaiser · 13-09-2019 5:14am

amandstu wrote: »

I have an interior wall which got damp as a result of a leak in the chimney stack above.

Even though that leak has been fixed the plaster will still not take paint without yellowing it immediately and in fact the plaster is still damp some 4 or 5 months later.

Beneath the plaster ,the rendering is dry but the plaster itself shows no sign of ever drying out.

Is the plaster actually damp or are you assuming that it is damp because of the yellowing?

The reason I ask, is because I had a similar chimney leak, and after fixing the chimney and re-plastering. Everytime I tried to paint certain patches, they immediately yellowed.

It wasn't until I came across photos taken before the re-plastering, that I realised the yellowing patches were directly on top of where black soot water had leaked through.

Something in the soot was obviously causing the yellowing so I painted the patched with oil based undercoat and then went over that with emulsion. The yellowing disappeared and hasn't come back.

It may not be your issue but thought I would mention it anyway

Souness · 13-09-2019 11:04am

Agree with chief kaiser, water stains will come through even if fully dry. The only way around this is to put an undercoat of stain blocker on the wall first.

But as said previously if the wall is not fully dried out I would not recommend sealing in dampness as this will eventually lead to the plaster blowing.

cnocbui · 13-09-2019 11:41am

Doesn't sound like the leak was actually fixed. What was the cause?

I had the same problem. My leak was caused by hair-line cracks in the render, which in most cases were hard to even see. I fixed it by applying a pricey flexible silicone based render intended for external insulation. That did the trick and the stack and plaster dried out completely. I put an efficient dehumidifier in the room which would pull about 5L of water from the air per day.

amandstu · 13-09-2019 2:52pm

cheif kaiser wrote: »

Is the plaster actually damp or are you assuming that it is damp because of the yellowing?

The reason I ask, is because I had a similar chimney leak, and after fixing the chimney and re-plastering. Everytime I tried to paint certain patches, they immediately yellowed.

It wasn't until I came across photos taken before the re-plastering, that I realised , the yellowing patches were directly on top of where black soot water had leaked through.

Something in the soot was obviously causing the yellowing so I painted the patched with oil based undercoat and then went over that with emulsion. The yellowing disappeared and hasn't come back.

It may not be your issue but thought I would mention it anyway

Yes I think we are discussing the same problem.

I am loathe to put an oil based paint on plaster which is actually damp.

There are areas on the wall that are dry but dark yellow in patches and that technique would work there.

I was fairly confident that I had fixed the leak in the chimney stack ,but if ,4 months later the plaster is still damp in a large area ,then maybe it is still there somehow.

If I can't find a leak in the stack then I feel I have to take away and replace all the damp plaster since I am confident that the rendering behind the plaster is bone dry.

amandstu · 13-09-2019 2:57pm

cnocbui wrote: »

Doesn't sound like the leak was actually fixed. What was the cause?

I had the same problem. My leak was caused by hair-line cracks in the render, which in most cases were hard to even see. I fixed it by applying a pricey flexible silicone based render intended for external insulation. That did the trick and the stack and plaster dried out completely. I put an efficient dehumidifier in the room which would pull about 5L of water from the air per day.

The wall is just below the chimney stack and ,yes the rendering is cracked in places
so I may well follow your suggestion and use something like Tech 7 on that fissure.

And maybe ,hacking away at the damp plaster will reveal other places where the rendering is cracked. (I can still hope

)

cnocbui · 13-09-2019 3:31pm

amandstu wrote: »

The wall is just below the chimney stack and ,yes the rendering is cracked in places
so I may well follow your suggestion and use something like Tech 7 on that fissure.

And maybe ,hacking away at the damp plaster will reveal other places where the rendering is cracked. (I can still hope )

I have about 1/4 of a tub of the render left and a full tub of the special primer for it, which I didn't end up using, but which I think might well fill and seal any fine cracks in render on it's own. You are welcome to them if you want. Both are white. I'm in Nth Tipp.

There might be enough of the render to do all of a smallish chimney.

Damp plaster

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